The invention relates to material for an expanded graphite gasket which gasket material is superior in sealing efficiency, handling properties and workability.
A sheet made of expanded graphite which sheet is formed by cold working of expanded graphite granules having memory effect against compaction is one of general gasket materials. The expanded graphite sheet has good sealing efficiency and is chemically stable, so that it well serves as gasket material made of non-asbestos compound. However, the expanded graphite sheet is not sufficient in tensile strength and toughness, so that the gasket material has the defect to be poor in handling property as readily cracked to fall at a portion of the sheet when subjected to pressure.
As a remedy for the defect, there has been used such gasket material formed by that a sheet metal, for example, of stainless steel having circular or rectangular protuberances is used as a core for reinforcing, and the expanded graphite sheets are fit over the core by rolling and fixed thereto by use of the protuberances.
Also, as another type of remedy, such gasket material has been used that the expanded graphite sheet and a sheet metal of stainless steel or the like as the core are overlapped and adhered to each other by use of resinous adhesive to thereby be reinforced.
In the former type of remedy, for fixing the expanded graphite sheet to the sheet metal core by use of the protuberances, the expanded graphite sheet is required to have a thickness for enclosing the protuberances and including the height thereof, inevitably to be thick more than 0.8 mm. This means that when applied to joints of high internal pressure, the gasket material has a defect to readily cause leakage of fluid.
Also, the core for reinforcing which has the protuberances needs to be inevitably more than 0.2 mm (200 .mu.m) in thickness, so that the gasket material having the core is poor in general-purpose properties when it is to be punched or simply cut for use. Also, the gasket material which is provided with the metal protuberances as aforesaid needs more than 39.2 MPa of clamping pressure in use.
In the foregoing another type of remedy, the core would be poor in strength when using an aluminum sheet metal, and readily corrosible when using common steel sheet metal, so that the core generally employs the stainless steel sheet metal. The gasket material when the expanded graphite sheet is adhered to the stainless steel sheet metal by use of adhesive has sufficient strength and is superior in corrosiveness with a thinner stainless steel, but has such a problem in adhesion properties that when the gasket material is repeatedly heated and cooled in a high temperature range, the expanded graphite sheet is readily peeled from the stainless steel sheet metal to be poor in reliability.
In the above method using the adhesive for fixing the expanded graphite sheet to the core for provision of gasket material, sealing material using foil in place of the sheet metal has been adopted. This gasket material has good workability, needs clamping pressure about 23.5 MPa in use and exhibits an excellent sealing efficiency, but has a problem in selection of materials for foils as that aluminum foil cannot compensate for fragility of expanded graphite, iron foil is readily corrosible and stainless foil (which is practically used in general) is likely to be peeled in a high temperature region.
Gasket material using expanded graphite without the above defects has been expected in the field.